package train48days;

import java.util.Scanner;

public class 年会抽奖 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long[] sum = new long[21];
        sum[0] = 1;
        sum[1] =1;
        sum[2] =2;
        long[] count = new long[21];
        count [0]=0;
        count [1]=0;
        count [2]=1;
        for (int i = 3; i <21 ; i++) {
            sum[i] =sum[i-1]*i;
            count[i]=(i-1)*(count[i-1]+count[i-2]);
        }
        while (sc.hasNext()){
            int n =sc.nextInt();
            double a=count[n];
            double b =sum[n];
            double ret = (a/b)*100;
            System.out.println(String.format("%.2f",ret)+"%");
        }
    }
}
